Among high frequency switch circuit devices employed in, for example, wireless data communications apparatuses or image transmission apparatuses, such apparatuses as, e.g., an antenna changeover switch and a signal modulation switch have different functions, so implementing them with a single device has been difficult. However, in view of reducing the number of semiconductor chips to install the apparatuses and simplifying the structure thereof, it becomes important to implement multiple functions with a signal device.
As an example of a semiconductor antenna changeover switch among the high frequency switch circuit devices for use in the conventional wireless data communications apparatuses or image transmission apparatuses, there has been known a semiconductor switch circuit device having a single input terminal and two output terminals, wherein distributed elements of transmission lines, capacitors and diodes are formed on a same surface on a semiconductor substrate (see, for example, Reference 1: E. Alekseev, et al., “77 GHz High-Isolation Coplanar Transmit/Receive Switch Using InGaAs/InP PIN Diodes”, 1998 IEEE GaAs IC Symposium).
In accordance with this configuration, each of the two output terminals is connected to a central point via a distributed element of a transmission line, a diode, and/or a capacitor and then to the input terminal via a distributed element of a transmission line.
Also in this configuration, the widths of the transmission lines are designed such that the impedances of the distributed elements of the transmission lines become identical to that of a system connected to the input and output terminals. In case a high frequency signal source is connected to the input terminal and a resistive load is coupled to each of the two output terminals, a high frequency input signal from the input terminal is switched to be outputted to the two output terminals by an on/off operation of the diodes. However, in case of switching on/off the high frequency input signal by connecting the high frequency signal source to one of the two output terminals and connecting a resistive load to the other output terminal, a part of the high frequency input signal is reflected by the input terminal and the distributed elements of the transmission lines led to the input terminal, thus increasing a loss of the high frequency signal.
With regard to the technique disclosed in Reference 1, if the semiconductor switch circuit having the one input terminal and the two output terminals is to be employed as a circuit for switching on/off the high frequency signal by connecting the high frequency signal source to one of the output terminals and the resistive load to the other, the input terminal and the distributed element of the transmission line led to the input terminal would not be necessary. However, to be used as a semiconductor switch circuit having one input terminal and two output terminals, the input terminal and the distributed elements of the transmission lines led to the input terminal are essential circuit elements, and there is a limit to reducing the loss of the high frequency signal by reducing the sizes of the input terminal and the distributed elements of the transmission lines led to the input terminal.
FIG. 13 provides an equivalent circuit diagram to illustrate a general circuit configuration of a semiconductor switch circuit including distributed elements of transmission lines, lumped elements of resistors and capacitors, at least one input terminal and two or more output terminals.
As shown therein, an input terminal 1, a distributed element 2 made of a transmission line whose length is about 2n−1 times λ/4 (n represents a natural number), a distributed element 4 made of a transmission line whose length is about 2n times λ/4 and an output terminal 6 are sequentially connected in series. A semiconductor 3 for switching operation is connected to the distributed elements 2 and 4, while a semiconductor 5 for a switching operation is connected to the distributed element 4 and the output terminal 6. Further, resistors 7 and 8 for controlling the semiconductors 3 and 5, respectively, are connected to a control terminal 9 and are grounded via a chip capacitor 10. Moreover, the input terminal 1, a distributed element 11 made of a transmission line whose length is about 2n−1 times λ/4, a distributed element 13 made of a transmission line whose length is about 2n times λ/4 and another output terminal 15 are sequentially connected in series. Also, a semiconductor 12 for switching operation is connected to the distributed elements 11 and 13 while a semiconductor 14 for switching operation is coupled to the distributed element 13 and the output terminal 15. Further, resistors 16 and 17 for controlling the semiconductors 12 and 14, respectively, are connected to a control terminal 18, and are grounded via a chip capacitor 19.
Referring to FIG. 14, there is shown a semiconductor switch circuit device obtained by forming the circuit in FIG. 13 on a semiconductor substrate.
In FIG. 14, the dielectric constant of the semiconductor substrate 20 is set to be 13.5, while its thickness is set to be 0.08 mm. Further, the widths of the transmission lines of the distributed elements 2, 4, 11 and 13 are set to be 0.054 mm; the resistor 7, 8, 16 and 17 are set to be 100Ω; the chip capacitors 10 and 19 are set to be 100 pF; and the sizes of the input terminal 1 and the output terminals 6 and 15 are set to be 0.1×0.12 mm.
FIG. 15 sets forth a graph to describe estimated values of transmission loss when a high frequency signal of a frequency ranging from 50 to 70 GHz is transmitted in the semiconductor switch circuit device configured as illustrated in FIG. 14.
In FIG. 15, a curve 15-1 represents a transmission loss of the high frequency signal transmitted from the input terminal 1 to the output terminal 15 when the turn-on resistances of the semiconductors 3 and 5 are set to be 2Ω and the turn-off resistances of the semiconductors 12 and 14 are set to be 2 kΩ. Further, curves 15-2 and 15-3 indicate a reflection loss of the high frequency signal at the input terminal 1 and a transmission loss, i.e., isolation of the high frequency signal transmitted from the input terminal 1 to the output terminal 6, respectively, under the same conditions. Moreover, a curve 15-4 represents a transmission loss of the high frequency signal transmitted from the input terminal 1 to the output terminal 15 when the turn-on resistances of the semiconductors 3 and 5 are set to be 2Ω; the turn-off resistances of the semiconductors 12 and 14 are set to be 2 kΩ; and the sizes of the input terminal 1 and the output terminals 6 and 15 are set to be as small as 0.074×0.02 mm. Further, curves 15-5 and 15-6 represent a reflection loss of the high frequency signal at the input terminal 1 and a transmission loss, i.e., isolation of the high frequency signal transmitted from the input terminal 1 to the output terminal 6, respectively, under the same conditions.
As can be seen from FIG. 15, when using the circuit device for switching a high frequency signal, if the sizes of the input terminal 1 and the output terminals 6 and 15 are extremely reduced, the reflection loss of the high frequency signal at the input terminal 1 can be reduced, but the transmission loss of the high frequency signal is not much influenced. Moreover, in order to connect the circuit externally, the input terminal 1 cannot be omitted therein.
FIG. 16 sets forth a graph to describe estimated values of transmission loss of a high frequency signal of a frequency ranging from 50 to 70 GHz when the high frequency signal is transmitted from the output terminal 6 to the other output terminal 15 by opening the input terminal 1 in the semiconductor switch circuit device configured as illustrated in FIG. 14.
In FIG. 16, a curve 16-1 represents a transmission loss of the high frequency signal transmitted from the output terminal 6 to the output terminal 15 when the turn-off resistances of the semiconductors 3, 5, 12 and 14 are set to be 2 kΩ. Further, a curve 16-2 indicates a reflection loss of the high frequency signal at the output terminal 6 under the same condition. Further, a curve 16-3 depicts a transmission loss, i.e., isolation of the high frequency signal transmitted from the output terminal 6 to the output terminal 15 when the turn-on resistances of the semiconductors 3, 5, 12 and 14 are set to be 2Ω. Moreover, a curve 16-4 indicates a transmission loss of the high frequency signal transmitted from the output terminal 6 to the output terminal 15 under the condition that: the turn-off resistances of the semiconductors 3, 5, 12 and 14 are set to be 2 kΩ; the sizes of the input terminal 1 and the output terminals 6 and 15 are set to be as small as 0.074×0.02 mm; and the input terminal 1 is opened. A curve 16-5 represents a reflection loss of the high frequency signal at the output terminal 6 under the same conditions, and a curve 16-6 depicts a transmission loss, i.e., isolation of the high frequency signal transmitted from the output terminal 6 to the output terminal 15 under the condition that: the turn-on resistances of the semiconductors 3, 5, 12 and 14 are set to be 2Ω; the sizes of the input terminal 1 and the output terminals 6 and 15 are set to be as small as 0.074×0.02 mm; and the input terminal 1 is opened.
As can be seen from FIG. 16, when using the conventional high frequency switch circuit in such a manner that a high frequency signal is inputted to one of the output terminals and outputted from the other output terminal, the reflection loss of the high frequency signal of the frequency ranging from 57 to 65 GHz at the output terminal 6 is reduced down to 7 dB or less due to a reflection at the input terminal 1 and so forth. However, if the sizes of the input terminal 1 and the output terminals 6 and 15 becomes extremely small, their influences upon the transmission loss of the high frequency signal transmitted from the output terminal 6 to the output terminal 15 decreases, so that the reflection loss of the high frequency signal at the output terminal 6 increases up to 20 dB or greater and the transmission loss of the high frequency signal from the output terminal 6 to the output terminal 15 is reduced down to about 2.1 dB or less. However, although the reflection loss and the transmission loss of the high frequency signal would be reduced without the input terminal 1, the input terminal 1 cannot be omitted in the high frequency switch circuit device because the input terminal 1 have to be connected externally in order to implement multiple functions with a single device. Thus, since the input terminal 1 is included therein, the transmission loss of the high frequency signal from the output terminal 6 to the output terminal 15 increases. Therefore, implementing a high frequency on/off switch as well as, e.g., an antenna changeover switch, a signal modulation circuit, and the like with a single device is difficult because their functions are different.